Commercial drink extraction apparatuses which can make coffee and the like by pouring hot water on a powdered drink material put in a filter (usually made of paper) so that extracted drink drips by its weight, have been widely used since its constitution is simple and it is not costly.
However, this type of apparatus has a disadvantage that it takes too much time, say 3 minutes, for extracting a cup of drink, since the drink is rendered to gravitational force drip. This is a serious problem in the case of an automatic vending machine because it forces the customer to wait for a long time, providing poor service and sales efficiency.
One way to overcome the disadvantage is to improve conventional self-weight filtering method, as shown in Japanese Utility Model Early Publication 60-57885. This prior art discloses a coffee extraction apparatus called "fresh brew coffee extraction apparatus", which employs a piston-cylinder means provided over a filter block for quickly filtering the coffee supplied and mixed with hot water and pressurized in the cylinder.
Another prior art, Japanese Patent Early Publication 61-149112, discloses an extraction apparatus which employs an air pump to provide pressurized air into the extraction chamber containing drink material and hot water so that the extracted drink may be filtered under the pressure of the air in a very short period of time.
Such piston means and air pump have been successful in making short the filtering time needed for the extracting drink from the mixture of the drink material and hot water.
However, the former of these has a disadvantage that it must have extra components such as a driving means for lifting or lowering the piston and a means for removing the used drink material, increasing complexity of the apparatus.
The latter also has another disadvantage that the air pump for generating the pressurized air results in not only complexity but also extra cost.
On the other hand, Japanese Utility Model Early Publication 1-8539 discloses such drink extraction apparatus as extracting the drink material in a filter of a material storing container.
In these apparatuses a pump is used in supplying hot water into a cartridge drink storage container through a discharge pipe and it is usually the case that the upper area of the drink material container is generally larger than the cross section of the discharging pipe, so that the pressurized hot water supplied from the discharge pipe tends to concentrate in the central portion of the container and that extraction is not done uniformly. Furthermore, in order to meet the requirement that the drink is vended in unit of cup, a hot water tank is also used in these apparatuses, as disclosed, for example, in Japanese Utility Model Early Publication 59-165081. Excessive hot water is overflown from the container through an overflow port back into the hot-water tank.
However, such tank is hazardous in that the boiling water might overflow from the overflowing port as the water filling the tank is boiled and is expanded or the boiling water showers out in fluctuation.